The invention relates to a projector-type headlamp for a vehicle, and more particularly to a low-beam headlamp.
Projector-type headlamps are frequently adopted as headlamps for vehicles.
As shown in FIG. 1, a projector-type headlamp comprises a light source 102 disposed on an optical axis Ax of the headlamp which extends in the longitudinal direction of a vehicle, a reflector 104 for reflecting light from this light source 102 in a forward direction close to the optical axis Ax, and a focusing lens 106 disposed forwardly of the reflector 104 and formed by a plano-convex lens whose front-side surface 106a is convex.
Further, a light shielding plate 108 is used to eliminate upward illuminating light in low beam by shielding part of the reflected light from the reflector 104. As shown in FIG. 1, the plate 108 is disposed between the focusing lens 106 and the reflector 104. For the reflected light with shielding, a luminous intensity distribution pattern P with a light-dark borderline CL is formed, as shown in FIG. 2.
With a conventional headlamp for a vehicle, the light-dark ratio of the borderline CL formed by the light shielding plate 108 becomes very high. If the light-dark ratio of the borderline CL is excessively high, the forward road surface can suddenly appear dark along the way, depending on the travel condition. A problem can happen when at night a vehicle approaches a flat road from a downward slope, which degrades the visibility of the far road surface. In addition, if a vehicle bounces to cause the borderline CL to move vertically even slightly, a driver of a vehicle on the opposite lane may be blinded by glare.
The invention has been devised in view of the above-described circumstances. The object is to provide a projector-type headlamp for a vehicle capable of addressing the problems of the light-dark ratio of the light-dark borderline in the luminous intensity distribution pattern for low beam light. The invention is capable of realizing the object without producing drawbacks such as irregular color produced by chromatic aberrations.
The above object is attained by forming a predetermined lens element on a front-side surface of a focusing lens of a headlamp.
A projector-type headlamp provided for a vehicle comprises: a light source disposed on an optical axis extending in a longitudinal direction of a vehicle; a reflector for reflecting light from the light source in a forward direction close to the optical axis; a focusing lens disposed forwardly of the reflector and formed by a plano-convex lens whose front-side surface is convex; and a light shielding plate interposed between the focusing lens and the reflector so as to eliminate upward illuminating light by shielding part of the reflected light from the reflector, wherein a lens element extending in a substantially horizontal direction along a line of intersection between the front-side surface and a horizontal plane including the optical axis is formed on the front-side surface of the focusing lens.
As long as the xe2x80x9clens elementxe2x80x9d has either a vertical deflection function or diffusion function, its cross-sectional shape, vertical width, and the number of the lens elements should not be limiting.
In a typical projector-type headlamp, the borderline in the luminous intensity distribution pattern for low beam, which is formed by a light shielding plate, is formed clearly by a light beam in a horizontal plane including the optical axis Ax of the headlamp. In a projector-type headlamp according to embodiments of the invention, the light-dark ratio of the borderline can be reduced by the lens element. The lens element is formed on the front-side surface of the focusing lens, which can be a plano-convex lens whose front-side surface is convex. The lens element extends in the horizontal direction along the line of intersection between the front-side surface and the horizontal plane including the optical axis.
A light beam transmitted through the lens element may cause irregular color to occur because of chromatic aberrations. The aberrations can affect the luminous intensity distribution pattern. However, the reflected light from the reflecting surface of the reflector is not incident upon the peripheral edge of the focusing lens in the region close to a line of intersection between the front-side surface and a horizontal plane, including the optical axis, in the front-side surface of the focusing lens. Therefore, the lens element of the embodiment of the invention does not cause the transmitted light beam to undergo chromatic aberrations to affect the luminous intensity distribution pattern.
In accordance with the invention, the projector-type headlamp can reduce the light-dark ratio of the borderline in the luminous intensity distribution pattern for low beam without producing drawbacks such as irregular color.
From the viewpoint of reducing the light-dark ratio of the borderline, a crimp or the like may be formed on the focusing lens instead of forming the lens element on the front-side surface of the focusing lens as in the invention. However, it is difficult to control deflection or diffusion of the transmitted light by means of a crimp or the like. Consequently, the light-dark ratio of the borderline CL can be insufficient reduced, or the light-dark ratio can be overly reduced to increase the upward illuminating light. Such upward illuminating light may temporary blind a driver in a vehicle on the opposite lane. In this respect, since the lens element can be formed on the front-side surface of the focusing lens, deflection and diffusion of the transmitted light can be controlled relatively accurately. Hence, the light-dark ratio of the borderline can be reduced to a necessary and sufficient level.
In addition, by forming a lens element on the front-side surface of the focusing lens, the following advantages can be obtained.
A focusing lens can be a plano-convex lens whose front-side surface is convex. After a lens material is filled in a mold having a cavity shape conforming to the shape of the front-side surface and is allowed to cure, the focusing lens can be manufactured by cutting its rear-side surface in a plane. If an attempt were made to form a lens element on the rear-side surface of the focusing leans, required cutting work would be more difficult. In contrast, the formation of the lens element on the front-side surface of the focusing lens as embodiments of the invention can be realized easily by adding the shape of the lens element to the mold. For this reason, in accordance with embodiments of the invention, the lens element can be formed with high accuracy at low cost.
Since the light-dark borderline is created by the light shielding plate partly shielding a light beam in a horizontal plane including the optical axis of the headlamp, the lens element is preferably formed to vertically straddle the line of intersection between the front-side surface of the focusing lens and the horizontal plane including the optical axis to reduce the light-dark ratio of the borderline.
In addition, if the lens element comprises an upwardly deflecting prism lens element, the light-dark ratio of the borderline can be reduced with high accuracy by setting its angle of upward deflection to an appropriate value.
Further, if a plurality of lens elements, each extending in a substantially horizontal direction, are formed vertically on the front-side surface of the focusing lens, the light-dark ratio of the borderline can be reduced in fine steps. Furthermore, a portion of those lens elements can be used to illuminate overhead signs.